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Structural Diversity in a New Series of Halogenated Quinolyl
Salicylaldimides-Based FeIII Complexes Showing Solid-State
Halogen- Bonding/Halogen···Halogen Interactions
Suchithra Ashoka Sahadevan, Enzo Cadoni, Noemi Monni, Cristina Saenz de Pipaon, JoseRamon Galan Mascaros, Alexandre Abherve,́ Narcis Avarvari, Luciano Marchio,̀ Massimiliano
Arca, and Maria Laura Mercuri
Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, S.S. 554 Bivio per Sestu, I09042 Monserrato,
Cagliari, Italy
Laboratoire MOLTECH-Anjou UMR 6200, UFR Sciences, CNRS, Université d’Angers, Bat. K, 2 Bd. Lavoisier, 49045 Angers,
France
Institute of Chemical Research of Catalonia, Barcelona Institute of Science and Technology, Avinguda Paısos Catalans 16, Tarragona
43007, Spain
Institució Catalana de Recerca i Estudis Avancats, Passeig Lluis Companys 23, Barcelona 08010, Spain
Dipartimento SCVSA, Università di Parma, Parco Area delle Scienze 17A, I43124 Parma, Italy

* Supporting Information
ABSTRACT: A new series of tridentate N-8-quinolyl-salicylaldimine ligands, Hqsal-5,7-X2 [X = Cl(1), Br(2), I(3)], halosubstituted at the 5,7 position of the aminoquinoline moiety and
their corresponding complexes with FeIII were synthesized and
formulated as [Fe(qsal-5,7-X2)(NCS)(MeO)]2·solv. (X = Cl (1a),
Br (2a), I (3a, solv = 1/2MeOH), [Fe4(qsal-5,7-X2)4(NCS)2(MeO)2]·solv. (X = Br (2b), I (3b; solv = 4CH2Cl2)) by singlecrystal X-ray diffraction analysis. 1a and 2a are isostructural dimers
where each FeIII metal ion, showing a distorted octahedral
environment, is bound by a N,N,O tridentate (qsal-5,7-X2)− (X =
Cl and Br) ligand, a N-coordinated SCN− anion, and a bridging
methanolate anion. 2b and 3b are centrosymmetric tetramers
where each FeIII is bound by three nitrogen atoms and three
oxygen atoms derived from a tridentate (qsal-5,7-X2)− (X = Br and I), a SCN−, a bridging methanolate anion, and a bridging μ2oxy moiety. In 3b, the iodine atoms dominate the packing interactions through the establishment of a halogen-bonding network.
The magnetic behavior of 1a−3a dimers and 2b−3b tetramers indicate the presence of strong antiferromagnetic interactions
between FeIII centers (S = 5/2), mediated by the alkoxy bridges. Experimental data can be modeled with an isotropic
Hamiltonian, H = −2J(S1 · S2) for dimers (J = −15 cm−1) and H = −2J(S2 · S3) − 2J′(S1 · S2 + S3 · S4), for tetramers (J = −24
cm−1, J′ = −11 cm−1). The magnetic behavior of 1a−3a dimers indicates the presence of strong antiferromagnetic interactions
between FeIII centers (S = 5/2), mediated by the alkoxy bridges. 2b and 3b show the same magnetic behavior since they contains
analogous bridges between paramagnetic centers, but for a linear tetramer. Density functional theory (DFT) calculations, based
on hybrid functional mPW1PW paralleled by the Def2SVP all-electron split-valence basis sets, support the experimental results,
showing that monomers could possibly show a spin crossover (SCO) behavior, even though the formation of complexes with an
even number of metal ions results in the strong antiferromagnetic interactions. Accordingly, broken symmetry DFT calculations
carried out on 1a clearly show that the antiferromagnetic coupling of the two HS FeIII centers results in the lowest energy
electron configuration of the complex.

■

INTRODUCTION

One of the most powerful strategies to design halogen-bonded
systems is based on the use of tectons, in particular,
metallotectons, namely, metal complexes bearing peripheral
halogen atoms, able to be involved in well identified noncovalent
intermolecular interactions, such as halogen bonds. Over the past
decade, halogen bonding (XB), a strong, specific, and highly

directional noncovalent interaction, has gained great interest
among the known noncovalent bonds, for the construction of
one-, two-, and three-dimensional (1D, 2D, and 3D) selfassembled supramolecular architectures.1−4 This interaction

plays a role as crucial as hydrogen bonding (HB)5 in driving
highly specific crystal packing patterns and several applications of
XB have been reported1 in various research areas such as
materials science and synthetic chemistry. Halogen···halogen
(XX) interactions are also a peculiar class of halogens bonds
interactions, which, although weak, play a key role in the
formation of supramolecular networks ranging from one- to
three-dimensional (1D to 3D) materials to self-assembled
monolayers and can be considered as a reliable supramolecular
tool in molecular self-assembly. 6−9 In this context the
combination of halo-substituted anilates, the 3,6-dihalo derivatives of 2,5-dihydroxybenzoquinone (H4C6O4), X2An2− (X = Cl,
Br, I), with paramagnetic metals has been shown to be
particularly successful.10−15 In the search of novel halosubstituted tectons where the halogen atoms can play a role on
the crystalline packing pattern and/or physical properties, we
focused our attention on the tridentate N-8-quinolyl-5-Xsalicylaldiminate (X = H, Hqsal) ligand and its halo-substituted
derivatives on the 5-salicylaldiminate moiety (qsal-X) (X = F, Cl,
Br, I), because of the interesting spin crossover (SCO) properties
shown by their FeIII/FeII complexes.16−21 Temperature-induced
spin transition in fact was observed in [Fe(qsal)2]NCS and
[Fe(qsal)2]NCSe22−25 with a wide thermal hysteresis loop of 140
and 180 K respectively, while switching the spin state upon
exposure to light (LIESST effect) was also found.24 Halogen
effects on the SCO behavior were reported in [FeIII(qsalX) 2] NC S·solvent ( X = F, Cl, Br; solvent =
1
/4CH2Cl2·1/2MeOH) complexes, as the spin transition temperature was found to increase on going from F to Br.17,26−31 Very
recently, an abrupt two-step SCO above room temperature32,33
was observed in the [FeII(qsal-Cl)2] complex due to the halogen
substitution on the salicylaldiminate moiety of the ligand that has
the potential to improve the SCO properties within FeII−SCO
systems. Therefore, the introduction of halogen atoms at certain
key positions of the metal complexes influences their physical
properties significantly, although keeping their structure
unaltered. In this work we investigate the influence of the
halogen substitution on the quinolyl moiety of the Hqsal ligand,
which has never been studied so far, with the aim to highlight
how a simple change in the positions of the halogen atoms in the
same ligand can dramatically change the crystal structure and
physical properties of the related metal complexes. We report
herein the synthesis and structural characterization of the novel
class of halo-substituted Hqsal-5,7-X2 ligands (X = Cl, 1, Br, 2, I,
3), shown in Chart 1, and their FeIII complexes: [Fe(qsalCl2)(NCS)(MeO)]2 (1a), [Fe(qsal-5,7-Br2)(NCS)(MeO)] 2
(2a), [Fe4(qsal-5,7-Br)4(NCS)2(MeO)2] (2b), [Fe(qsal-5,7I2)(NCS)(MeO)]2, (3a,·1/2MeOH), and [Fe4(qsal-5,7-I2)4Chart 1. Structure of Hqsal-5,7-X2 Liganda

a

X = Cl (1), Br (2), I (3).

(NCS)2(MeO)2] (3b,·4CH2Cl2). The magnetic properties of
the 1a−3a and 2b−3b complexes are also reported.

■

RESULTS AND DISCUSSION

Synthesis of Hqsal-5,7-X2 Ligands and Their Fe III
Complexes. An overview of the synthetic procedure of the
Hqsal-5,7-X2 ligands is shown in Scheme 1.
The halo-substituted Hqsal-5,7-X2 ligands were prepared in
good yields (48−89%) by treating 5,7-dihalo-8-aminoquinoline
in EtOH with salicylaldehyde and glacial acetic acid. The
synthesis of the Hqsal-5,7-X2 ligands was performed according to
the synthetic pathway shown in Scheme S1 in Supporting
Information. The first stage of the process is a simple formation
of an imine, starting from amine and aldehyde, at room
temperature and with good yields despite the substituents
used. The reaction is carried out in ethanol and in the presence of
acetic acid. Acetic acid was used both for increasing the
electrophilicity of the carbonyl aldehyde group, given the low
nucleophilicity of the aromatic amine, and for favoring the water
elimination in the second stage. The reagents and the products
are poorly soluble in ethyl alcohol, and therefore reaction times
of almost 24 h are required for the complete disappearance of the
amines as reported in Scheme S2 in Supporting Information.
More details on the synthesis34−37 are given in Supporting
Information.
The FeIII complexes, 1a−3a and 2b−3b, were synthesized
according to the general synthetic strategy recently reported for
analogous complexes 20 (Scheme 2).
These complexes were obtained by carefully layering the
ligands 1−3 with Et3N in CH2Cl2 and on top FeCl3·6H2O and
NaSCN in a 1:1 ratio, dissolved in MeOH. Electrospray
ionization mass spectrometry (ESI-MS) spectra recorded on
freshly prepared CHCl3/MeOH solutions, in the 100−2000 m/z
mass range, showed only the molecular ions, which can be
assigned to [Fe(qsal-5,7-X2)2]+ monomeric species [X = Cl
(1c+), Br (2c+), and I (3c+)]. Mass spectra recorded on solutions
with concentration values at the upper solubility limit (10 mg/
mL) and lower values of needle voltage of 4500 V did not show
dimeric forms (vide infra). Therefore, to improve peak
resolution, spectra were recorded in the 100−1000 m/z mass
range. The isotopic patterns of the ligands 1−3 and of the
monomeric species 1c + 2c + and 3c + are reported in Supporting
,
,
Information (Figures S1−S2).
Structural Studies. Among the ligands, only single crystals
of 3 could be obtained by recrystallization of the crude product in
dichloromethane, confirming the expected composition (Figure
S3).
Single crystals of the iron complexes were obtained by slow
diffusion of ligand in dichloromethane and FeIII salt with NaSCN
in methanol. The X-ray diffraction analysis unexpectedly
established the complexes to be dimers or tetramers according
to Scheme 2 and Table 1.
The presence of halogen atoms on the ligands periphery
expands the types of interactions that can be exchanged by the
iron complexes.38,39 Here, we will analyze the influence of the
halogen substitution (Cl, Br, I) on the second coordination
sphere and crystal packing.
The complexes 1a and 2a crystallize in the triclinic space group
P1̅; 2b crystallizes in monoclinic space group P21/c. The
molecular structure of 1a is reported in Figure S4. The molecular
structures of 2a, 3a, 2b, and 3b are reported in Figures 1, 2, and 3.
A summary of X-ray crystallographic data for 3, 1a−3a, and 2b−
3b are reported in Table S1, and selected bond distances (Å) and

Scheme 1. Overview of the Synthetic Procedure of Hqsal-5,7-X2 Ligands

Scheme 2. General Synthetic Scheme for 1a−3a, 2b−3b Complexesa

a

X = Cl (1), Br (2), I (3); a = dimer; b = tetramer.

Table 1. Summary of the Obtained FeIII Complexes
FeCl3·6H2O + NaSCN
X = Cl
[Fe(qsal-5,7-X2)(NCS)(MeO)]2 dimer
[Fe4(qsal-5,7-X2)4(NCS)2(MeO)2] tetramer

Br

I

1a

2a
2b

3aa
3bb

a

Structurally characterized in 3a·1/2MeOH. bStructurally characterized
in 3b·4CH2Cl2.

angles (deg) for 1a−3a and 2b−3b are reported in Tables S2−
S7.

Compounds 1a and 2a are isostructural, and their molecular
features can therefore be described together. Both complexes lie
on an inversion center and half dimer represents the asymmetric
unit. The FeIII metal is in a distorted octahedral environment, and
it is bound by a N,N,O tridentate ligand, a SCN− anion, and a
bridging methanolate anion. For the tridentate ligand, the Fe−N
bond distances are significantly longer (0.13−0.25 Å) than the
remaining bond distances, and the shortest distance is that
between the metal and the phenolate moiety, Table S2 in
Supporting Information. The SCN− anion is bound to the metal
center through the nitrogen atom, and consistently, it exhibits a

Figure 1. Molecular structure of 2a (symmetry code ′ = −x; 1 − y; 1 − z) and 3a (symmetry code ′ = 2 − x; 1 − y; −z, ′′ = 1 − x; −y; 1 − z). Thermal
ellipsoids are drawn at the 30% probability level. Color code: C = gray, Cl = green, Br = brown, O = red, S = yellow, Fe = orange, N = blue, H = white.

linear coordination geometry. The asymmetric unit of
compound 3a comprises two half dimeric units and one
methanol molecule of crystallization (Figure 1). The overall
structural arrangement is nevertheless similar to that of 1a and
2a, since the presence of the iodine on the periphery of the
aromatic rings has a negligible influence on the iron coordination
environment. The methyl alcohol molecule forms a hydrogen
bond with the oxygen atom of the phenolate moiety, O(11). In
1a−3a, the metal−metal distance is approximately 3.15 Å. The
crystal packing of 1a and 2a is reported in Figure S5 and Figure 2.
Adjacent molecules exchange different types of interactions,
namely, Cl···Cl (3.39 Å) and Br···Br (3.51 Å) with symmetry
related halogen atoms, CH···S with the aromatic ring and the
SCN− anion and π−π stacks with adjacent bromoquinoline rings.
The crystal packing of 3a is more complex due to the presence of
two different molecular entities and the solvent of crystallization.
In this system, the presence of the iodine atom with respect to the
bromine and chlorine in 1a and 2a expands the possible types of
interactions that can be formed between adjacent molecules. In
fact, I(22) and I(21) both interacts with S(1T) of the thiocyanate
group. The geometry of the I(22)···S(1T) interaction (3.49 Å) is
consistent with the presence of a halogen bond, whereas the
geometry of the I(21)···S(1T) interaction (3.56 Å) presumably
occurs through the negatively charged corona on iodine toward
the terminal sulfur consistent with the presence of a chalcogenide
bond.1,4,40
2b and 3b are centrosymmetric tetramers where the two
outermost metal have a different coordination environment than
the two innermost metals (Figure 3).
In 3b, four dichloromethane molecules of crystallization per
tetrameric complex are present. In both systems Fe(1) is bound
by three nitrogen atoms and three oxygen atoms derived from a
N,N,O tridentate ligand, a SCN− anion, a bridging methanolate,
and a bridging oxy moiety. Differently, Fe(2) is bound by two
nitrogen atoms and four oxygen atoms derived from a N,N,O
tridentate ligand, two bridging oxy moieties, and a bridging
methanolate anion. In both compounds, the Fe(1)−Fe(2) and
Fe(2)−Fe(2)′ bond distances are 3.07 and 2.96 Å, respectively.
The crystal packing of 2b is reported in Figure 4. Ideally, the
molecules form layers by means of π−π stacks, CH···S, and CH···
C/N interactions between the aromatic ring and the SCN−

anion. These layers interact by forming halogen bond (Br(3)···
Br(4), 3.62 Å) and CH···Br (3.77 Å) interactions between
symmetry related molecules.
In 3b, the iodine atoms dominate the packing interactions, as
shown in Figure 5. According to the geometries of the
interactions, the negative corona of I(1) interacts with the σhole of I(4) of a symmetry related molecule. Likewise, the lone
pair distribution of S(1) interacts with the σ-hole of I(3).1,4,40
Hence, I(3) acts as an XB donor with respect to the carbon atom
of an adjacent SCN− anion. Hence I(2), I(3), and I(4) act as XB
donors, whereas I(1) acts as an XB acceptor. Dichloromethane
molecules of crystallization are also involved in weak interactions
among adjacent complex molecules.
Different views of the crystal packing of 3b are reported in
Figure S6. In all ligand systems, the aromatic moieties linked by
the imino group are not coplanar since they form a dihedral angle
in the 31−41° range. In 2b and 3b, the tridentate ligands
positioned on the same side with respect to the Fe4O4 core form
π−π stacks with the quinoline and phenolate residues. The
shortest contact is between the aromatic rings of the phenolate
groups (3.4−3.5 Å range), whereas the distances between the
quinoline groups is approximately 3.6 Å for 2b and greater than
3.7 Å for 3b.
Magnetic Measurements. In these series, compounds type
a (dimers) and b (tetramers) are magnetically identical, if we
consider the intermolecular magnetic interactions as negligible.
Indeed, their magnetic behavior is indistinguishable within
experimental error. Therefore, we only describe the magnetic
properties of 1a and 2b, as representatives of these two magnetic
structures.
The χT product for 1a at room temperature is 5.01 emu K
mol−1, lower than the expected value for the spin-only
contribution of two high spin (HS) FeIII S = 5/2 centers (χTHS
≈ 8.750 emu K mol−1), but significantly higher than the spin-only
contribution of two low spin (LS) FeIII S = 1/2 centers (χTLS. ≈
0.750 emu K mol−1). This confirms the HS state of the FeIII
centers and suggests the presence of strong antiferromagnetic
interactions between them, mediated by the alkoxy bridges. In
the 2−300 K range, χT decreases with temperature (Figure 6,
left), reaching values close to zero at very low temperatures. The
experimental data can be fitted to the Hamiltonian:

≈ 1.50 emu K mol −1 ). In this case, the appropriate
phenomenological Hamiltonian is
H = −2J(S2 ·S3) − 2J′(S1·S2 + S3·S4)

Figure 2. Portion of the crystal packing of 2a (a and b) and 3a (c), with
the methanol molecule of crystallization highlighted. Dashed lines
represent short interactions between symmetry related molecules.
Selected weak interaction distances are indicated in Å.

H = −2J(S1·S2)
where S1 = S2 = 5/2. The best fit (Figure 6, left) was found for g =
2.09, J = −21 K (−14.6 cm−1), with the addition of a small
paramagnetic impurity, equivalent to ∼2% of the total spin
carriers.
The magnetic behavior for 2b is similar, since it contains
analogous bridges between paramagnetic centers, but now in a
linear tetramer. The room temperature χT product is 8.50 emu K
mol−1. This value can only be assigned to four HS FeIII centers,
antiferromagnetically coupled (χTHS ≈ 17.50 emu K mol−1, χTLS

where S1 = S2 = S3 = S4 = 5/2. The temperature dependence of
the χT product was satisfactorily reproduced with parameters: g
= 2.03, J = −35 K (24.3 cm−1), J′ = −16 K (11.1 cm−1), and a
paramagnetic impurity equivalent to ∼2.5% of the total spin
carriers (Figure 6, right). It is particularly significant the fact that
the shape of the curve can be reproduced only if J > J′. We found a
ratio of 2 between both exchange parameters as optimum to
reproduce the data. This can be rationalized if we look into the
Fe−O−Fe angles. Whereas the Fe1−O−Fe2 bridging angles are
asymmetric (≈ 98° and 105°), the two Fe2−O−Fe2 angles are
almost identical, forming a perfect square. This permits a better
overlap between the magnetic orbitals, and a stronger
antiferromagnetic superexchange in the central bridge.
DFT Calculations. In order to investigate the electronic
structure and reactivity of the ligands 1−3 and the relevant
iron(III) complexes, quantum-mechanical (QM) calculations
were carried out at the density functional theory (DFT) level.41
Previous theoretical investigations showed that the correct
modeling of high/low spin equilibria at the DFT level depends
dramatically on the choice of the functional,42 which can
unevenly favor one of the two spin states. In particular, it was
observed that the pure functionals PW9143,44 and BLYP45 favor
the LS state, while the paradigmatic hybrid functional
B3LYP,46−48 featuring a 20% Hartree−Fock (HF) exchange,
favors the HS state.37 Kepp comparatively examined 12 different
functionals and demonstrated that the B3LYP* hybrid functional
(HF exchange 15%)49,50 provides an accurate evaluation of the
HS-LS energy gap for 30 different SCO iron complexes.51 This
notwithstanding, in the peculiar case of qsal-X− (qsal-X− =
monosubstituted quinolylsalicylaldiminate; X = H, OMe, F, Cl,
Br, I) FeIII tris-complexes, the B3LYP* functional was recently
proven52to overestimate the HS−LS enthalpy difference
ΔHSCO. In this work, based on the very good results achieved
in the past on a variety of both organic53−55 and inorganic
systems,56−58 we turned to test the hybrid functional mPW1PW
by Adamo and Barone,59 paralleled by the Def2SVP all-electron
split-valence BS, including polarization functions.60
Whatever the combination of BSs and functional, HS and LS
configurations show different structural features, in particular, as
far as the metal ion is involved, so that a comparison between
theoretically optimized and structural metric parameters allows
for the attribution of the correct spin state. A validation of the
computational setup chosen for this work was therefore carried
out by comparing the structural bond distances and angles
determined for the complex [Fe(qsal-F)2]+ (4+), isolated in
4(NCS),17 featuring an LS at 100 K and a HS FeIII center at 270
K, with the corresponding optimized metric parameters. An
examination of the bond distances involving the central metal ion
shows that on passing from LS to HS the Fe−N distances are
sensibly modified [average values 1.960(2) and 1.983(2) Å at
100 and 270 K,14 respectively], while the Fe−O bond lengths
remain almost unaltered [average values 1.875(2) and 1.866(2)
Å at 100 and 270 K,14 respectively]. DFT optimized distances are
in very good agreement with the structural ones and display the
trend found experimentally on passing from LS to HS
configurations [LS: Fe−N, 1.973; Fe−O 1.857; HS: Fe−N,
2.173; Fe−O, 1.898 Å]. Notably, the uncorrected total electronic
energies of the LS and HS configurations calculated for 4+ in the
gas phase differ by only 2.80 kcal mol−1, while the enthalpy

Figure 3. Molecular structure of 2b (left) and 3b (right), with thermal ellipsoids drawn at the 30% probability level. Solvent molecules and hydrogen
atoms were removed for clarity. Symmetry code ′ = 1 − x; 1 − y; 1 − z. Color code C = gray, Br = brown, I = violet, O = red, S = yellow, Fe = orange, N =
blue, H = white.

Figure 4. Portion of the crystal packing of 2b. Dashed lines represent
short interactions between symmetry related molecules. Selected weak
interaction distances are indicated in Å.

contribution ΔHSCO to the spin-crossover (SCO) amounts to
3.84 kcal mol−1, in agreement with the temperature-controlled
SCO behavior observed experimentally.14 The structures of the
neutral protonated compounds Hqsal-5,7-X2 (1−3) and the
corresponding O-deprotonated (qsal-5,7-X2)− anions were
optimized at the same level of theory. A comparison of the
metric parameters calculated for 3 with the corresponding ones
determined by single crystal X-ray diffraction (see above) clearly
shows an excellent agreement. In particular, it is worth noting
that the C−I distances are optimized at values extremely close to
the experimental ones (optimized C−I distance = 2.109 Å). Also
the formation of the intramolecular O12−H12···N2 bond is
reproduced correctly with an optimized O···N distance only

slightly overestimated [calculated 2.598 Å; structural value
2.652(4) Å]. In agreement with the crystal structure analysis, the
aminoquinoline moiety is twisted with respect to the plane of the
phenyl ring (τ = 44.63°). On passing from 3 to the corresponding
deprotonated form qsal-5,7-I2−, the metric parameters remain
almost unvaried, with a small decrease in the τ dihedral angle [τ =
39.98° for (qsal-5,7-I2)−] and the loss of planarity of the 2hydroxyphenylmethanimine moiety. In the deprotonated form,
Kohn−Sham (KS) frontier molecular orbitals can be envisaged
with large contributions from the lone pairs of electrons located
on the two nitrogen and the oxygen atoms (KS-HOMO-6,
HOMO-3, and HOMO-1 for (qsal-5,7-I2)−; Figure 7].
These atoms feature remarkable negative natural61,62 charges
Q (QN1 = −0.463, QN2 = −0.504, and QO12 = −0.645 |e|) and are
therefore all available to interact with the iron(III) ions. On
passing from qsal-5,7-I2 − to the corresponding brominated and
chlorinated anions, the natural charges are basically unvaried
[(qsal-5,7-Cl2)−: QN1 = −0.465, QN2 = −0.499, and QO12 =
−0.650 |e|; (qsal-5,7-Br2)−: QN1 = −0.464, QN2 = −0.500, and
QO12 = −0.647 |e|), thus indicating similar donor abilities of the
three donor atoms. On varying the nature of the halogen
substituents, KS-HOMO-1, KS-HOMO-3, and KS-HOMO-6
keep the same composition in terms of their constituent atomic
orbitals, their eigenvalues becoming progressively slightly more
stable on passing from (qsal-5,7-I 2 ) − to (qsal-5,7-Cl 2 ) −
[eigenvalues ε: KS−HOMO-1: −2.082, −2.156, −2.230;
HOMO-3: −3.504, −3.570, −3.605; HOMO-6: −4.760,
−4.734, and −4.601 eV for (qsal-5,7-Cl2) − (qsal-5,7-Br2) −
,
,
and (qsal-5,7-I2)−, respectively].
DFT calculations have been extended to the monomer
cationic complexes [Fe(qsal-5,7-X2)2]+ [X = Cl (1c+), Br
(2c+), I (3c+)], identified in solution by mass spectrometry
(see above). These complexes, although not isolated in the solid
state, represent interesting model complexes of the potential spin
crossover (SCO) behavior. In order to model the possible
electron configurations, both the HS (S = 5/2, sixtuplet) and LS
(S = 1/2, doublet) configurations63 were modeled for the three
FeIII complexes. The optimized structures of complexes 1c+−3c+
show the central ion in a distorted octahedral coordination
achieved by the two N1 and N2 atoms and by the O atoms

Figure 5. Highlights on the interaction exchanged by the iodine atoms in
3b. Dashed lines represent short interactions between symmetry related
molecules, distances are indicated in Å.

(Figure S8 for 1c+ in the HS state). Notably, upon coordination
the phenyl and the quinolyl rings tend to to a larger degree of
coplanarity as compared to the free ligand in order to maximize
the interaction to the metal ion (for example, τ = 15.73° for 1c+ in
the HS state).
In Table 2, the Fe−N and Fe−O bond lengths optimized for
1c+, 2c+, and 3c+ both in the LS and HS states are listed, showing
that the nature of the halogen affects only marginally the bond
distances, which depend as expected on the spin state.
An examination of the crystal structures of compounds 1a, 2a,
and 3a clearly shows that Fe−O distances fall in the range 1.92−
1.94 Å, Fe−N1 bond lengths are all around 2.18 Å, while Fe−N2
distances are slightly shorter (2.13 Å). Therefore, the structural

Accordingly, the total electronic energies calculated for HS and
LS complexes 1c+−3c+ in the gas phase testify to a larger stability
of HS as compared to LS, with energy differences ΔESCO of 3.0,
3.2, and 3.5 kcal mol−1 for 1c+, 2c+, and 3c+, respectively, which
are only slightly larger than those calculated for 4 at the same
level of theory. A thermochemical analysis shows that by taking
into account the zero point energy (ZPE) corrections and the
thermal corrections to enthalpy, the same trend is confirmed
(ΔHSCO = 4.07, 4.28, and 4.52 kcal mol−1 for 1c+, 2c+, and 3c+,
respectively). The sum of electronic and thermal free energy
calculated for HS and LS model complexes in the gas phase
(ΔGSCO = 7.59, 7.91, and 7.90 kcal mol−1 for 1c+, 2c+, and 3c+,
respectively) shows that the entropy term is essentially
independent of the nature of the halogen (ΔSSCO = 1.18 ×
10−2, 1.22 × 10−2, and 1.13 × 10−2 kcal mol−1 for 1c+, 2c+, and
3c+, respectively), so that T1/2 depends exclusively on the
enthalpy term (|ΔHLS‑HS/ΔSLS‑HS| = 344, 351, and 359 for 1c+,
2c+, and 3c+, respectively). The trend in the ΔHSCO values was
confirmed when solvation was implicitly considered at the IEFPCM SCRF level64 (ΔESCO = 2.49, 2.78, and 3.11 kcal mol−1;
ΔHSCO = 3.50, 3.73, and 4.62 kcal mol−1 for 1c+, 2c+, and 3c+, in
CHCl3, respectively).
These results strongly testify to an SCO nature of the
complexes 1c+−3c+, both in the solid state and in chloroform
solution. Therefore, theoretical results suggest that while
monomers could possibly show a SCO behavior, the formation
of complexes with an even number of metal ions results in the
strong antiferromagnetic interactions, evidenced experimentally
(see above), that prevent any SCO behavior in the solid state. In
order to verify this hypothesis, the electronic structure of 1a was
investigated at the same level of theory, in the open- and closedshell singlet configurations (2S + 1 = 1, 1asing), as an independent
HS FeIII−FeIII complex without coupling (2S + 1 = 11, 1aHS‑HS),
and eventually as an antiferromagnetic singlet (1aafc). The latter
configuration was obtained by using a broken symmetry
approach65 from a guess of the ground state defined by molecular
fragments, including one [Fe(qsal-5,7-X2)]2+ ion with five
unpaired α-spin electrons (sextet), and another one with five
β-spin electrons (sextet). The resulting wave function was
optimized to avoid restricted/unrestricted spin instabilities and
the geometry of the complex was finally reoptimized. In Table 3
some selected bond lengths are listed for the examined electronic
configurations, along with the total electronic energies and spin
densities (Figure S10) calculated for 1asing, 1aHS‑HS, and 1aafc.
A comparison of the optimized bond lengths and angles clearly
shows that only the configurations of 1aHS‑HS and 1aafc reproduce
reliably the coordination pattern at the iron(III) centers. In
addition, the closed-shell singlet displays, as expected, a RHF/
UHF instability. The total electronic energies calculated for
1aHS‑HS and 1aafc are consistent with the antiferromagnetic state
being the ground state, in perfect agreement with the magnetic
measurements discussed above. Notably, the spin densities of
±4.29 |e|/au3 (Figure S10) are in excellent agreement with five
unpaired electrons on each FeIII center, since part of the spin
density delocalizes onto the ligands.

■

CONCLUSIONS

A new series of the tridentate N-8-quinolyl-salicylaldimine
ligands Hqsal-5,7-X2 (X = Cl(1), Br(2), I(3)) and their
corresponding complexes with FeIII, formulated as [Fe(qsal5,7-X2)(NCS)(MeO)]2·solv. (X = Cl (1a), Br (2a), I (3a)),
[FeIII (qsal-5,7-X ) (NCS) (MeO) ]·solv. (X = Br (2b), I (3b;
4

parameters clearly point to a HS configuration of the complexes.

2 4

2

2

solv = 4 CH2Cl2), have been synthesized and structurally

Figure 6. Thermal variation of χMT versus T plots for 1a (left) and 2b (right). In red, the fitting obtained with the following parameters: g = 2.09, J = −21
K (−14.6 cm−1) (1a) and g = 2.03, J = −35 K (24.3 cm−1), J′ = −16 K (11.1 cm−1), (2b).

Figure 7. Isosurface drawings of KS-HOMO-6 (MO 83), KS-HOMO-3
(MO 86), and KS-HOMO-1 (MO 88) with large contributions from the
LPs on the N and O donor atoms in (qsal-5,7-I2)−. Cutoff value = 0.05 |
e|.

Table 2. Fe−N and Fe−O Bond Distances Optimized for the
Model Complexes 1c+−3c+ at DFT Level in the Gas Phase in
the LS and HS Configurationsa
1c+
HS

LS

Fe−N2
Fe−N1
Fe−O1
Fe−N2
Fe−N1
Fe−O1

2c+

3c+

2.131
2.192
1.906
1.949
1.994
1.856

2.129
2.192
1.908
1.947
1.994
1.858

2.126
2.192
1.911
1.944
1.994
1.860

Labels of the (qsal-5,7-X2)− ligands as in Figure 2 (X = Cl, Br, and I,
for 1c+, 2c+, and 3c+, respectively).
a

characterized. 1a and 2a are isostructural dimers where each FeIII
metal is bound by the N,N,O tridentate qsal-5,7-X2 (X = Cl and
Br) ligand, a SCN− anion, and two bridging methanolate anions
in a distorted octahedral environment. The SCN− anion exhibits
a linear geometry since it is bound to the metal center through
the nitrogen atom. Several Cl···Cl (3.39 Å) and Br···Br (3.51 Å)
halogen intermolecular interactions with symmetry related
halogen atoms, CH···S with the aromatic ring and the SCN−
anion, and π−π stacks with adjacent bromoquinoline rings occur
between adjacent molecules. In 3a iodine atoms interact through

a linear I22···S1T geometry with S1T of the SCN− group via
halogen bonding. 2b and 3b are centrosymmetric tetramers
where each FeIII is bound by three nitrogen atoms and three
oxygen atoms deriving from the tridentate qsal-5,7-X2 (X = Br
and I), a SCN− anion, a bridging methanolate, and a bridging oxy
moiety. Unexpectedly, the halo-substitution at the 5,7 position of
the aminoquinoline moiety yields dimers and tetramers instead
of the mononuclear complexes with a dramatic change of the
magnetic properties of the reported complexes, on going from
SCO magnetic behavior observed in the mononuclear complexes
to strong antiferromagnetic interactions between FeIII centers (S
= 5/2), mediated by the alkoxy bridges in dimers and tetramers
herein reported.66,67 DFT calculations support the structural
finding, showing that monomers could possibly show an SCO
behavior, even though the formation of complexes with an even
number of metal ions results in strong antiferromagnetic
interactions. DFT clearly shows as well that the antiferromagnetic coupling of the two HS FeIII centers in 1a results in the
lowest energy electron configuration of the complex.
In conclusion the search for halogen-bonded systems where
halogen-bonds dominate the structure and influence the physical
properties of a given material still represents a challenge in
material science, even though the results reported in this work
show that the proper choice of the halogen substitution on the
ligand coordinated to the metal can provide chemists with a
versatile strategy for the crystal-engineering design of new
compounds with novel physical properties. Further studies will
involve the replacement of halogen atoms with different
substituents in order to investigate their role, both at the
electronic and supramolecular level, in determining the
molecular packing pattern and the related physical properties.

■

EXPERIMENTAL SECTION

Materials. All manipulations were performed in air with reagent
grade solvents. All organic chemicals were purchased from TCI
(Zentek) and were used without further purification, and inorganic
chemicals were purchased from Sigma-Aldrich and used as received. FTIR spectra were performed on KBr pellets and collected with a Bruker
Equinox 55 spectrophotometer. Melting points were obtained on a
Kofler hot stage microscope and are uncorrected. Elementary analyses
were performed by −CHNS/O PerkinElmer 2400 series II. The
aminoquinoline derivative was separated by a chromatographic column
(25 mm × 180 mm) filled with DAVISIL silica gel (40−63 m), packed
with a Buchi C-670 cartridge.

Table 3. Selected Bond Lengths Calculated for 1a in the Singlet Configuration (1asing), with Two Independent HS FeIII Ions
without Coupling (1aHS‑HS), and as an Antiferromagnetic Singlet (1aafc)a
1asing
2S + 1
Fe−N2
Fe−N1
Fe−O1
Fe−O2/O2′
Fe−N1T
ETOT
spin density on FeIII

1aHS‑HS

1aafc

1
1.946
1.962
1.900
1.919/1.933
1.881
−7177.6703036
0, 0

11
2.196
2.206
1.948
1.981/2.042
1.972
−7177.7815725
+4.30, +4.30

1
2.196
2.206
1.948
1.981/2.042
1.972
−7177.7827629
+4.29, −4.29b

Struct.
2.139
2.183
1.920
1.981/2.033
2.106

a

For each configuration the total electronic energy ETOT (Hartree) and the spin densities (|e|/au3) on the metal ions are also reported. bFigure S10.
Labels of the ligand donor atoms as in Figure 2.
Synthesis of 5,7-Dichloro-8-aminoquinoline. A solution of sulfuryl
chloride (60.0 mmol) in 12.5 mL of glacial acetic acid was added slowly
with stirring to a solution of 8-aminoquinoline (4.38 g, 30.4 mmol) in 21
mL of glacial acetic acid cooled to 10 °C by an ice bath. The mixture was
then warmed gradually to room temperature and finally was heated for
25 min on the steam bath at 70−75 °C. Then, the reaction mixture was
quenched by a solution of 20 g of sodium acetate in 150 mL of water.
The precipitated crude product was removed by filtration and dried in
air. Yield: 4.98 g (77%) melting point: 183−184 °C. ESIMS(+): 213.00
m/z (M + H+) with the expected isotope distribution.
Synthesis of 2-[(5,7-Dichloroquinolin-8-ylimino)-methyl]-phenol
(Hqsal-5,7-Cl2), 1. 5,7-Dichloro-8-aminoquinoline (3.34 g, 15.7 mmol),
salicylaldehyde (2.02 g, 24.3 mmol), and glacial acetic acid (0.34 mL)
were dissolved in 40 mL of dry ethanol. The reaction mixture was stirred
at room temperature for 14 h. The end of the reaction was verified by
TLC (2:8 of diethyl ether/petroleum ether). When the reaction was
completed, the mixture reaction was filtered, washed, and dried in air.
Yield: 3.74 (74.9%). Melting point: 201 °C with decomposition. Elem
anal. Calcd for C16H10Cl2N2O (found), mass %: C, 60.59 (59.73); H,
3.18 (2.94); N, 8.33 (8.55). FTIR: νmax(KBr)/cm−1 3435 (νOH),
3057, 2921 (νCH), 1621 (νC N). 1H NMR (DMSO-d6/DCl): δ =
13.45 (s), 9.41 (s), 9.25 (dd), 8.89 (dd), 8.06 (s), 7.86 (m), 7.78 (dd),
7.74 (td), 7.61 (s), 7.37 (d), 7.28 (td). ESIMS(+): 317.1 m/z (M + H+),
with expected isotope distribution.
Synthesis of 5,7-Dibromo-8-aminoquinoline. N-Bromosuccinimide (2.44 g, 13.0 mmol) was added slowly to a stirred solution of 8aminoquinoline (1.0 g, 6.9 mmol) and 1.4 g, of NaClO4/SiO2 a 1:4 ratio
in CH2Cl2 (20 mL). The reaction mixture was stirred at room
temperature for 5−10 min, and the progress was controlled by TLC
(50:50 of diethyl-ether/petroleum ether). When the reaction was
completed, the mixture was filtered, and the catalyst washed with
CH2Cl2 (2 × 10 mL). Then, the combined organic layer was washed
with water, dried over anhydrous sodium sulfate, and concentrated
under reduced pressure using a rotary evaporator. Further purification
was carried out by flash chromatography on silica gel (diethyl ether/
petroleum ether: 4/6). Yield: 1.39 (66.9%). Melting point: 143 °C.
ESIMS(+): 303.1 m/z (M + H+) with expected isotope distribution.
Synthesis of 2-[(5,7-Dibromoquinolin-8-ylimino)-methyl]-phenol
(Hqsal-5,7-Br2), 2. 5,7-Dibromo-8-aminoquinoline (1.60 g, 5.3 mmol),
salicylaldehyde (1.00 g, 8.1 mmol), and glacial acetic acid (0.1 mL) were
dissolved in dry ethanol (40 mL). The reaction mixture was stirred at
room temperature for 22 h. The end of the reaction was verified by TLC
(diethyl ether/petroleum ether 2:8). When the reaction was completed,
the mixture reaction was filtered, washed, and dried in air. Yield: 1.9 g
(89.0%). Melting point: 180 °C with decomposition. Elem anal. Calcd
for C16H10Br2N2O (found), mass %: C, 47.33 (46.68); H, 2.48 (2.23);
N, 6.90 (6.64). FTIR: νmax(KBr)/cm−1 3435 (νOH), 3049, 2962
(νCH), 1621 (νC N). 1H NMR (DMSO-d6/DCl): δ = 13.32 (s), 9.30
(s), 9.19 (dd), 8.84 (dd), 8.41 (s), 7.84 (m), 7.76 (dd), 7.72 (td), 7.54
(s), 7.36 (d), 7.27 (td). ESIMS(+): 404.9 m/z (M + H+), with expected
isotope distribution.
Synthesis of 5,7-Diiodo-8-aminoquinoline. Potassium iodide (1.0 g,
6.0 mmol) was added slowly to a stirred solution of 8-aminoquinoline
(0.43 g, 3.0 mmol), NaIO4 (1.28 g, 6.0 mmol), and NaCl (0.69 g, 12.0

mmol) in 40 mL of acetic acid/water (9/1). The reaction mixture
changed from orange to black, and then it was stirred at room
temperature for 3 h. When the reaction was completed to the mixture
was added 30 mL of water, extracted with CH2Cl2 (3 × 20 mL). Then,
the combined organic layer was dried over anhydrous sodium sulfate and
concentrated under reduced pressure using a rotary evaporator. Further
purification was carried out by flash chromatography on silica gel
(diethyl ether/petroleum ether: 1/1). Yield: 0.66 g (44.0%) Melting
point: 144−145 °C with decomposition. ESIMS(+): 397.1 m/z (M +
H+).
Synthesis of 2-[(5,7-Diiodoquinolin-8-ylimino)-methyl]-phenol
(Hqsal-5,7-I2), 3. 5,7-Diiodo-8-aminoquinoline (0.58 g, 1.5 mmol),
salicylaldehyde (0.39 g, 1.6 mmol), and glacial acetic acid (0.1 mL) were
dissolved in dry ethanol (20 mL). The reaction mixture was stirred at
room temperature for 14 h. The end of the reaction was verified by TLC
(2/8 of diethyl ether/petroleum ether). When the reaction was
completed, the mixture reaction was filtered, washed, and dried in air.
Yield: 0.35g (48.0%). Melting point: 173−174 °C with decomposition.
Elem anal. Calcd for C16H10I2N2O (found), mass %: C, 38.43 (39.12);
H, 2.02 (2.31); N, 5.60 (5.32). FTIR: νmax(KBr)/cm−1 3441 (νOH),
3057, 2921 (νCH), 1612 (νC N). 1H NMR (DMSO-d6/DCl): δ =
13.19 (s), 9.23 (s), 9.17 (dd), 8.95 (s), 8.75 (dd), 7.86 (m), 7.81 (m),
7.62 (s), 7.44 (d), 7.34 (td). Mass spectrometry (MS): 501.1 m/z (M +
H+).
Synthesis of [Fe(qsal-5,7-Cl2)(NCS)(MeO)]2 (1a). Compound 1 (20.0
mg, 0.06 mmol) was dissolved in CH2Cl2 (5 mL) with Et3N (8.36 μL,
0.06 mmol) to give a yellow solution and was layered at the bottom of
test tube. FeCl3·6H2O (8.10 mg, 0.03 mmol) in 1.5 mL of MeOH and
NaSCN (2.68 mg, 0.03 mmol) in 1.5 mL of MeOH were sonicated for 5
min to give dark purple solution and were carefully layered on top of the
above layer. A blank solution of MeOH (1 mL) was layered in between
the above-mentioned solutions. Dark red crystals were formed at the
interface after 5 days. Yield = 54.5%. Elem Anal. Calcd for
C36H24Cl4Fe2N6O4S2 (found), mass %: C, 46.88 (47.12); H, 2.62
(2.54); N, 9.11(8.87), Cl 15.38(15.22), O 6.94(6.95), S 6.95(6.56), Fe
12.11(12.01). FTIR: νmax(KBr)/cm−1 2920 (νAr−H), 2061 (νC N),
1605 (νC N). MS (ESI+): m/z 688 [Fe(qsal-Cl2)]+.
Synthesis of [Fe(qsal-5,7-Br2)(NCS)(MeO)]2 (2a), [Fe4(qsal-Br)4(NCS)2(MeO)2] (2b). The synthetic procedure of 2a was the same as 1a
but using 2 (25.0 mg, 0.06 mmol) instead of 1. The use of a very slight
excess of Et3N (10.03 μL, 0.07 mmol) yielded 2b. Yield = 56.7% (2a)
and 48% (2b). Elem Anal. Calcd C36H24Br4Fe2N6O4S2 2a (found), mass
%: C, 39.31 (39.12); H, 2.2 (2.31); N, 7.64 (7.32) Br, 29.05(28.62); O
5.82(5.78), S 5.83(5.56), Fe 10.15(10.91) Elem Anal. Calcd
C68H42Br8Fe4N10O8S2 2b (found), mass %: C, 39.77 (39.12); H, 2.06
(1.99); N, 6.82 (6.32) Br, 31.12(30.52); O 6.23 (5.83), S 3.12 (3.42), Fe
10.88 (10.71). FTIR: νmax(KBr)/cm−1 2922 (νAr−H), 2049 (νC
N), 1603 (νC N). MS (ESI+): m/z 866 [Fe(qsal-Br2)]+.
Synthesis of [Fe(qsal-5,7-I2)(NCS)(MeO)]2 (3a), [Fe4(qsal-5,7-I 2)4(NCS)2(MeO)2] (3b). The synthetic procedure of 3a was the same as 1a
but using 3 (30 mg, 0.06 mmol) instead of 1. The use of a very slight
excess of Et3N (10.03 μL, 0.07 mmol) yielded 3b. Yield = 49.34% (3a)
and 41% (3b). Elem Anal. Calcd C37H28Fe2I4N6O5S2 3a (found), mass
%: C, 33.66 (33.75); H, 2.14 (2.39); N, 6.37 (6.22) I, 38.45(37.54); O

6.06 (7.1), S 4.86 (4.74), Fe 8.46(8.26) Elem Anal. Calcd
C72H50Cl8Fe4I8N10O8S2 3b (found), mass %: C, 31.22 (30.24); H,
1.82 (1.85); N, 5.06 (4.77), Cl 10.24 (8.47) I, 36.66(34.54); O 4.62
(4.35), S 2.32 (2.18), Fe 8.07 (7.6). FTIR: νmax(KBr)/cm−1 2919
(νAr−H), 2054 (νC N, 3a), 2046 (νC N, 3b), 1601 (νC N). MS
(ESI+): m/z 1054 [Fe(qsal-I2)]+.
X-ray Crystallography. Single crystal data were collected with a
Bruker APEX DUO diffractometer with a Quazar MX Multilayer Optics
diffractometer (Mo Kα radiation; λ = 0.71073 Å) at 100 K (1a, 2a, and
2b) and with a Bruker Smart APEXII at 200 K (3a and 3b). A summary
of data collection and structure refinement for 1a−3a, 2b, and 3b are
reported in Table 1. The intensity data were integrated from several
series of exposures frames (0.3° width) covering the sphere of reciprocal
space.68 Absorption correction were applied using the program
SADABS.69 The structures were solved by the dual space algorithm
implemented in the SHELXT code.70 Fourier analysis and refinement
were performed by the full-matrix least-squares methods based on F2
implemented in SHELXL-2014.71 Graphical material was prepared with
the Mercury 3.972 program. CCDC 1812729−1812733 contain the
supplementary crystallographic data for this paper.
ESI-MS. Mass spectra were recorded on a triple quadruple QqQ
Varian 310-MS mass spectrometer using electrospray ionization (ESI)
technique. The mass spectra were recorded in positive ion mode in the
m/z 50−1000 range. The sample solutions (10 mg/L) were prepared in
CH3OH and infused directly into the ESI source using a Varian HPLC
pump with a flow rate of 50 μL/min. Needle, shield, and detector were
kept at 4500, 600, and 1450 V respectively. Pressure of nebulizing and
drying gas was 40 PSI, housing and drying gas temperature was 60 and
250 °C, respectively.
Magnetic Measurements. Magnetic measurements were carried out
on polycrystalline powder samples. Each sample was secured inside a
tight gel capsule and transferred into the sample compartment of a
Quantum Design MPMS-XL-7T SQUID magnetometer (Quantum
Design, Inc., San Diego, CA, USA). Magnetic measurements were
carried out under an applied field of 1000 Oe in the 2−300 K
temperature range. Pascal’s constants were used to estimate the
diamagnetic corrections for compounds.
DFT Calculations. Theoretical calculations were performed at the
DFT36 level with the Gaussian 09 commercial suite of programs73 on the
neutral compounds 1−3, the corresponding O-deprotonated compounds (qsal-5,7-X 2)− (X = Cl, Br, I), the monomer iron(III) complex
cations [Fe(qsal-5,7-X2)2]+ (1c+, 2c+, 3c+ for X = Cl, Br, I), and the
complex cation [Fe(qsal-F)2] + (4 +). 14 The hybrid functional
mPW1PW54 was adopted along with all-electron Schafer, Horn, and
Ahlrichs split-valence plus polarization basis sets (BSs) for all atomic
species in the Def2SVP Weigend formulation.55 The molecular
geometry optimizations were performed starting from structural data,
when available. For all iron(III) complexes, the calculations were carried
out both in the high spin (HS, S = 5/2) and the low spin (LS, S = 1/2)
configurations. Tight SCF convergence criteria (SCF = tight keyword)
and fine numerical integration grids [Integral(FineGrid) keyword] were
used. The ZPE and enthalpy corrections at 298.15 K were calculated for
1c+−3c+ and added to the total electronic energy differences ΔESCO to
calculate the enthalpy differences ΔHSCO between HS and LS. Entropy
corrections to the energy differences between HS and LS (ΔSSCO) were
calculated from the sum of electronic and thermal enthalpies and free
energies (ΔGSCO). It was presumed that the temperature difference
from 298.15 K to the room temperature was negligible. The calculations
were extended to 1a in the closed- and open-shell singlet configurations
(1asing, 2S + 1 = 1), in the configuration featuring two uncoupled FeIII
HS ions (1aHS‑HS, 2S + 1 = 11) and in the antiferromagnetic complex
(1aafc, 2S + 1 = 1, with 5 α- and 5 β-spin electrons on the two metal
centers) following a broken symmetry approach. Accordingly, for 1aafc
six fragments were defined at the geometry optimized for 1aHS‑HS: two
[FeIII(qsal-5,7-X2)]2+ fragments (2S + 1 = 6, charge 2+), two CH3O−
anions (2S + 1 = 1, charge −1), and two SCN− anions (2S+1 = 1, charge
−1). Using the “guess = fragment” option, the wave functions of the
fragments were combined to form a guess of the wave function of the
whole complex. An MO calculation was then completed for the total
complex, and the stability of the resulting wave function was verified

(stable = opt). The complex was eventually reoptimized and the stability
of the wave function verified again. The nature of the minima for all the
optimized structures were verified by harmonic frequency calculations.
Atomic charges were calculated in the framework of the natural bonding
orbital (NBO)56,57 analysis at the optimized geometries at the same level
of theory. In order to account for the influence of the solvent on the
electron configurations of the compounds, calculations were also carried
out in the presence of CHCl3, implicitly taken into account by means of
the polarizable continuum model (PCM) approach (linear response;
nonequilibrium solvation) in its integral equation formalism variant
(IEF-PCM), which describes the cavity of the solute within the reaction
field (SCRF) through a set of overlapping spheres.59 The optimized
geometries were investigated by means of the program GaussView
5.0.9.74 In order to investigate KS-MO isosurfaces, the Molden 5.775
program was used in a macOS compiled version.76

■

ASSOCIATED CONTENT

* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.cgd.8b00753.
Additional figures and tables as mentioned in the text
(PDF)
Accession Codes

CCDC 1812729−1812733 and 1816966 contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: mercuri@unica.it; fax: (+39)0706754486; tel: (+39)
0706754486.
ORCID

Jose-Ramon Galan Mascaros: 0000-0001-7983-9762
Narcis Avarvari: 0000-0001-9970-4494
Luciano Marchio: 0000-0002-0025-1104
̀
Maria Laura Mercuri: 0000-0002-4816-427X
Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS

This work was supported in Italy was supported by the
Fondazione di Sardegna-Convenzione triennale tra la Fondazione di Sardegna e gli Atenei Sardi, Regione Sardegna-L.R. 7/
2007 annualità 2016-DGR 28/21 del 17.05.2015 “Innovative
Molecular Functional Materials for Environmental and Biomedical Applicatons” and INSTM. The work in France was
supported by the CNRS, the University of Angers, the Erasmus
program (mobility grant to N.M.), and the RFI Regional project
LUMOMAT (grant to A.A.). The work in Spain was supported
́
by the Spanish Ministerio de Economia y Competitividad
(MINECO) through Project CTQ2015-71287-R and the Severo
Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319, the
Generalitat de Catalunya (2014-SGR-797), and the CERCA
Programme. The authors wish to greatly acknowledge Dr.
Matteo Atzori for the synthesis and crystal structure of the Hqsal5,7-I2 derivative, which was first reported in his Ph.D. thesis
(Award for the best Thesis of Inorganic Chemistry 2015, given
by Società Chimica Italiana, Inorganic Division, MercuriAvarvari Supervisors).

■

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